T 0319/21 (FLUOROSULFONYLIMIDE AMMONIUM SALT/Nippon Soda) 14-04-2023

1. Priority right, Article 87(1) EPC

The patent in suit was filed as a divisional application (DA) from the earlier application PA (parent application) which claims priority from P1, the priority document.

1.1 In view of G 1/15 (order), the patent enjoys (partial) priority for processes as claimed using the values of p identical to the integers 0, 1, 2, 3 and 4.

Processes as claimed using pure substances of NH4F, NH4F(HF), NH4F(HF)2, NH4F(HF)3, NH4F(HF)4 thus enjoy the right of partial priority.

1.2 P1 referred to "alkali metal hydroxide". Paragraph [0028] of P1 reads (emphasis added) as follows:

"Examples of the alkali metal compound used in the cation exchange reaction include hydroxides such as LiOH, NaOH, KOH, RbOH and CsOH, carbonates such as ..., hydrogen carbonates such as ..., chlorides such as ..., bromides such as ..., fluorides such as ..., alkoxide compounds such as ..., hydrides such as ..., and alkyllithium compounds such as .... Of these compounds, a hydroxide is preferable. By using a hydroxide, ammonia is produced as a by-product in the cation exchange reaction, and therefore by removing this ammonia under reduced pressure, the equilibrium can be adjusted to a state that promotes the cation exchange reaction...."

Paragraph [0028] thus discloses hydroxides as an example of alkali metal compounds. Some specific examples of alkali metal hydroxides are also disclosed. These specific examples do not restrict the generic disclosure that the alkali metal compounds can be (alkali metal) hydroxides to the specific examples of the alkali metal hydroxides.

1.3 Paragraph [0028] also teaches the use of reduced pressure, particularly in combination with the use of hydroxides.

Moreover, alkali metal hydroxides have the valency of 1 since the (outermost) s-orbital contains only one electron. The selection of the valency is thus implicitly contained in the restriction to alkali metal hydroxide.

No multiple selection is apparent.

The subject-matter of claim 1 thus enjoys the right to the claimed priority inasmuch as it relates to the embodiments disclosed in the priority document.

2. Grounds for opposition, Article 100(c) EPC

2.1 Fresh ground under Article 100(c) EPC / Article 123(2) EPC

The objection under Article 100(c) EPC / Article 123(2) EPC was not raised during the opposition proceedings. Since the proprietor does not give consent to the introduction of this fresh ground, it is not admitted into the appeal proceedings (G 10/91 Headnote, point 3.).

2.2 Ground under Article 100(c) EPC / Article 76(1) EPC

The objection under Article 100(c) EPC / Article 76(1) EPC was already filed in opposition proceedings as a then fresh ground for opposition (see letter dated 2 November 2020, page 4). It is essentially based on the same arguments as were put forth against the validity of the priority claim.

The opposition division did not admit this fresh ground into the proceedings because it did not consider the ground to be prima facie relevant for the same reasons related to the validity of the priority claim and because of its conclusion that the priority claim was valid. Therefore the opposition division exercised their discretion according to the correct principles and in a reasonable way.

There is thus no reason to overturn the decision of the opposition division not to admit the then fresh ground for opposition into the proceedings.

3. Sufficiency of disclosure, Article 100(b) EPC

The subject-matter of claim 1 does not specify any desired technical effect.

It is well-established case law that an objection of insufficient disclosure cannot legitimately be based on an argument that the patent did not enable a skilled person to achieve a technical effect which is not defined in the claim (see T 1311/15, Reasons 5.2.).

3.1 The appellant argues specifically that the patent in suit lacked information and a limitation regarding the organic solvent.

The patent in suit discloses the claimed process in examples 3 to 5. All three examples disclose a suitable type of solvent. The skilled person would therefore obtain enough guidance for selection of the solvent.

3.2 The appellant argues further that the patent in suit did not provide guidance for a solvent-free process, which was covered by the subject-matter of claim 1.

Despite bearing the burden of proving the alleged facts, the appellant did not provide any evidence that a solvent-free process would not work even if one of the reactants were liquid and therefore this speculation cannot be taken into account.

3.3 The appellant argues that some solvents could be used because a product free of metal impurities could not be achieved.

However, a product free of metal impurities is not claimed in the subject-matter of claim 1 and therefore this argument must fail.

3.4 The appellant argues that ammonium bis(fluorosulfonyl)imide could not be dissolved in any solvent.

However, the subject-matter of claim 1 does not require that the ammonium bis(fluorosulfonyl)imide be dissolved in a solvent prior to the cation exchange reaction.

The appellant did not provide evidence that the cation exchange reaction was not possible for this compound, and therefore this argument cannot be taken into account.

3.5 The appellant argues that replicating the reproduction of example 4 did not achieve the yield disclosed in example 4. When some parameters such as the molar amount of the reactants were changed, the yield dropped further as demonstrated in document E1.

This argument fails simply because the subject-matter of claim 1 does not claim a minimum yield. Moreover, document E1 shows that a skilled person had no apparent trouble in selecting an alternative solvent.

3.6 Document E1 also discloses that the mixture was refluxed under reduced pressure. A skilled person thus had no apparent difficulty in understanding and implementing this feature.

The patent is therefore sufficiently disclosed.

4. Novelty, Article 100(a) EPC with Article 54(1) and (2) EPC

The appellant bases their objection on D4, example 4 which discloses the production of ammonium di(fluorosulfonyl)imide with the fluorinating agent NH4F(HF)p, where p=0. Since p=0 is contained in the priority document, the effective date is the priority date of the patent in suit.

Since both documents claim the same priority date and at least the patent in suit's priority is valid, D4 cannot be a prior art document within the meaning of either Article 54(2) EPC or Article 54(3) EPC.

The subject-matter of claim 1 is thus novel.

5. Inventive step, Article 56 EPC

The patent is directed to a process for producing a fluorosulfonylimide salt.

The parties consider D1/D1bis, embodiment 5 to constitute the closest prior art.

This is directed to the production of bis(fluorosulfonyl)imide and is thus suitable as a starting point for an inventive step objection.

According to the respondent, the patent in suit aims to provide an improved process for producing bis(fluorosulfonyl)imide salts via a shorter and therefore more efficient reaction.

The appellant disagrees and argues that it is ambiguous what is to be understood by "under reduced pressure". This feature should thus not be considered as a difference and therefore the only difference is to use KOH instead of KF. Since E1 demonstrated that it was not possible to achieve a higher purity at an acceptable yield, the problem considered to be solved by the patent in suit should be merely to provide an alternative.

The appellant argues that in view of D2 (or D3), the skilled person knows that potassium fluoride could be replaced by alkali hydroxides.

The feature "under reduced pressure" is broad. However, it does not encompass ambient pressure as argued by the appellant. It cannot therefore be ignored.

Even if, to the benefit of the appellant, it were accepted that the objective technical problem was the provision of an alternative and the skilled person would consider replacing potassium fluoride with an alkali metal hydroxide, the subject-matter of claim 1 could not be achieved.

Paragraph [0057] of D1/D1bis discloses neutralising the bis(chlorosulfonyl)imide acid by merely adding an approximately equimolar amount of ammonium fluoride and mixing at room temperature. Under the given reaction conditions, it is not apparent that this would result in the comprehensive formation of ammonium bis (fluorosulfonyl)imide. Firstly, the added ammonium fluoride cannot be considered to provide enough fluorine to the reaction system for complete fluorination. Moreover, it is not clear whether merely mixing at room temperature yields the same product as reaction under reduced pressure (i.e. refluxing according to the patent in suit).

Finally, if the potassium fluoride were replaced by an alkali metal hydroxide, as suggested by the appellant, the fluorine which completes the fluorination in D1/D1bis, embodiment 5, would not be added (see paragraph 9 of D1/D1bis).

6. In view of the objective in D1/D1bis of producing bis(fluorosulfonyl)imide, it is immediately apparent that a skilled person would not, when starting therefrom, consider a measure which had the consequence of the reaction system not receiving enough fluorine to complete the fluorination.

The presence of an inventive step must therefore be acknowledged.